1. Field of the Invention
The present invention relates to a seismic isolator for exhibits that will protect exhibits at museums, art galleries, etc., from earthquakes and other vibrations.
2. Description of the Prior Art
FIG. 8 is a perspective view of a conventional seismic isolator that uses linear guide rails. A plurality of lower linear guide rails 2 are lined up in a single linear direction and fixedly attached to the upper surface of a support stand 1, which is fixed to the top of a foundation.
A plurality of upper linear guide rails 4 are lined up in another linear direction, that is, a direction at a right angle to the lower linear guide rails 2 mentioned above, and fixedly attached to the lower surface of a pedestal carrying an exhibit, a display case, or other seismic isolation object 3.
A coupling block 5 is placed between each of the lower linear guide rails 2 and the upper linear guide rails 4. the lower section of the coupling block 5 is supported, through a ball, so that it can move smoothly along the lower linear guide rails 2. The upper section of the coupling block 5 supports, through a ball and together with the upper linear guide rails 4, the seismic isolation object 3 so that it can slide smoothly in the longitudinal direction of the upper guide rails 4.
With this, the seismic isolation object 3, within the length of the lower linear guide rails 2 and the upper guide rails 4, is supported so that it can move smoothly in all horizontal directions. However, the ends of plural numbers of coiled restoring springs 6, placed in parallel to the lower linear guide rails 2 and the upper linear guide rails 4, are attached to the upper surface of the support stand 1 and the lower surface of the seismic isolation object 3. They protect by restoring the seismic isolation object 3 to its original position before it moved horizontally, and by relieving vibrations in the horizontal direction.
FIG. 9 is a vertical cross sectional view of another conventional seismic isolator that uses curved faces. A plurality of support blocks 9 are installed in the lower surface of a lower face plate 7 by set screws 8, and the lower face plate 7 is fixed to the top of a foundation that is not shown, through the support blocks 9. Sphere support caps 10 are fixed to the upper surface of the lower face plate 7, and spheres 11 are rotatably supported on top of the support caps 10, through ball bearings.
An upper face plate 12 is placed above the lower face plate 7, and a seismic isolation object, not shown, such as a pedestal carrying an exhibit or a display case, is installed on top of the upper face plate 12.
A support plate 14 is fixedly attached to the lower surface of the upper face plate 12, and a curved surface 1II with a concave spherical shape is formed on the lower side of the plate 14. The curved surface 13 is set on top of the sphere 11, supporting the upper face plate 12.
A bolt 15 is installed in the center of the lower surface of the upper face plate 12. The bolt 15 is passed through a large hole 16 bored in the center of the lower face plate 7, and a stop plate 17 is installed at the lower end. A cover 18 is installed around the periphery of the upper face plate 12.
When the seismic isolator of FIG. 9 above is exposed to the vibrations of an earthquake, etc., the upper face plate 12 can move freely in all horizontal directions through a support plate 14 set on top of the sphere 11. Horizontal vibrations of the upper face plate 12 are relieved by a restorative force that arises from the weight loaded onto the sphere 11 from the curved surface 13. A seismic isolation object such as a pedestal carrying an exhibit or a display case, installed on top of the upper face plate 12 is thus protected from vibrations.
Three or more coupling blocks 5 are required with the conventional seismic isolator shown in FIG. 8, in order to maintain horizontal the seismic isolation object 3 supported on the lower linear guide rails 2. Supposing a displacement amplitude of 200 mm in a single direction is required, the lower linear guide rails 2 and the upper linear guide rails 4 of 200 mm each will be needed on both sides of the three or more coupling blocks 5. Thus a problem exists in miniaturizing the seismic isolator.
Further, coupling blocks are not used in the conventional seismic isolator shown in FIG. 9. The sphere 11 is sandwiched between the lower face plate 7 and the upper face plate 12. Supposing a displacement amplitude of 200 mm in a single direction is required, since a displacement is provided from the vertical deviations, the curved surface 13 must have a radius of 200 mm or more. Thus problems exist in miniaturizing the seismic isolator, and in its high cost since a very large expense will be incurred in manufacturing the support plate 14 furnished with the curved surface 13.
The object of the present invention is to solve these problems by providing a seismic isolator for exhibits that are small, that can relieve large vibrations, and that is inexpensive.
The present invention relates to a flat-type seismic isolator for exhibits comprising: a lower face plate installed on a foundation; an upper face plate that is installed to the lower surface of a seismic isolation object and placed above the lower face plate; an intermediate plate placed between the upper face plate and the lower face plate; and elastic restoring means and damping means provided for returning the plates to their original positions and placed in a lower area between the lower face plate and the intermediate plate and an upper area between the intermediate plate and the upper face plate, respectively, wherein: in the lower area, one lower linear guide rail is disposed in the center of the area and guide rails and rollers are disposed at both ends parallel to the lower linear guide rail for smoothly moving the intermediate plate with respect to the lower face plate in one linear direction; and in the upper area, one upper linear guide rail is disposed in the center of the area and guide rails and rollers are disposed at both ends parallel to the upper linear guide rail for smoothly moving the upper face plate with respect to the intermediate plate in one linear direction, the lower linear guide rail and the upper linear guide rail orthogonally crossing each other, the guide rails and the rollers in the lower area and the upper area orthogonally crossing each other. Through the guide rails and rollers, the upper face plate can move smoothly in all horizontal directions, and by the elastic restoring metals, the upper face plate is restored to its original position, and horizontal vibrations are relieved. The height of the entire device is reduced to a small size.
In a further aspect, the seismic isolator for exhibits set forth above further comprises damping means of a magnet disposed in the lower area between the lower face plate and the intermediate plate and in the upper area between the intermediate plate and the upper face plate. By use of only a magnet, vibration displacement can easily be damped.